What is the difference between these two python idioms?
if data is not None:
return data
if data: return data
Asked
Active
Viewed 8,169 times
8
Niklas Rosencrantz
- 25,640
- 75
- 229
- 424
-
1See: http://stackoverflow.com/questions/6497166/problem-with-pythons-is-none-test and http://stackoverflow.com/questions/26595/is-there-any-difference-between-foo-is-none-and-foo-none – Josh Lee Jun 14 '13 at 21:26
1 Answers
16
The latter will also reject False, 0, [], (), {}, set(), '', and any other value whose __bool__ method returns False, including most empty collections.
The None value in Python is often used to indicate the lack of a value. It appears automatically when a function does not explicitly return a value.
>>> def f():
... pass
>>> f() is None
True
It’s often used as the default value for optional parameters, as in:
def sort(key=None):
if key is not None:
# do something with the argument
else:
# argument was omitted
If you only used if key: here, then an argument which evaluated to false would not be considered. Explicitly comparing with is None is the correct idiom to make this check. See Truth Value Testing.
Josh Lee
- 171,072
- 38
- 269
- 275